One who eats cereals produced from grains such as wheat or oats recites the Beracha of Mezonot, whereas cereals produced from corn require either the Beracha of Ha'adama or She'hakol (depending on whether or not the corn underwent a fundamental transformation over the course of processing). Which Beracha does one recite over cereals containing both corn and grains?
The Gemara in the sixth chapter of Masechet Berachot establishes the basic principle that any food product containing one of the five principal grains (wheat, barley, oats, rye and spelt) requires a Mezonot, even if the grain constitutes a minority of the food's overall composition. So long as the grain is included for the purpose of taste or nourishment, it is seen as the dominant ingredient, regardless of its proportion to the rest of the food item, thus requiring the recitation of Mezonot. If, however, the grain substance is added purely as a binding agent, to maintain the food's shape and consistency, we disregard the grain's presence in determining which Beracha to recite over the given product (Shulchan Aruch, Orach Chayim 208:2). For example, gefilte fish and certain types of meatballs contain flour or matza meal to keep the fish or meatballs intact; over these foods one would recite She'hakol, as we disregard the flour in determining the proper Beracha. This principle applies as well to foods such as tortilla chips and corn chips, which include wheat starch as a binding agent.
Therefore, breakfast cereals that contain flour for the purpose of enhancing taste or adding nourishment would require the recitation of Mezonot, even if corn is the primary ingredient. Examples of this kind of cereal are Honeycomb, Honeycrunch, Alphabits, Apple Jacks and Froot Loops. All these cereals require the Beracha of Mezonot.
If, however, a grain substance such as wheat starch is added to a cereal purely as a binding agent, and not to add flavor or nourishment, one would recite She'hakol over that cereal. Examples of this kind of cereal are Reese's Puffs, Trix, Cocoa Puffs, Cookie Crisp, Cocoa Dots and Crunchies. Over these cereals, one would recite the Beracha of She'hakol, and not Mezonot.
